// Tencent is pleased to support the open source community by making RapidJSON available.
//
// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.
//
// Licensed under the MIT License (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
// http://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.

#ifndef RAPIDJSON_BIGINTEGER_H_
#define RAPIDJSON_BIGINTEGER_H_

#include "../rapidjson.h"

#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && defined(_M_AMD64)
#include <intrin.h> // for _umul128
#if !defined(_ARM64EC_)
#pragma intrinsic(_umul128)
#else
#pragma comment(lib, "softintrin")
#endif
#endif

RAPIDJSON_NAMESPACE_BEGIN
namespace internal
{

    class BigInteger
    {
    public:
        typedef uint64_t Type;

        BigInteger(const BigInteger& rhs)
            : count_(rhs.count_)
        {
            std::memcpy(digits_, rhs.digits_, count_ * sizeof(Type));
        }

        explicit BigInteger(uint64_t u)
            : count_(1)
        {
            digits_[0] = u;
        }

        template <typename Ch>
        BigInteger(const Ch* decimals, size_t length)
            : count_(1)
        {
            RAPIDJSON_ASSERT(length > 0);
            digits_[0]                         = 0;
            size_t       i                     = 0;
            const size_t kMaxDigitPerIteration = 19; // 2^64 = 18446744073709551616 > 10^19
            while (length >= kMaxDigitPerIteration)
            {
                AppendDecimal64(decimals + i, decimals + i + kMaxDigitPerIteration);
                length -= kMaxDigitPerIteration;
                i += kMaxDigitPerIteration;
            }

            if (length > 0)
                AppendDecimal64(decimals + i, decimals + i + length);
        }

        BigInteger& operator=(const BigInteger& rhs)
        {
            if (this != &rhs)
            {
                count_ = rhs.count_;
                std::memcpy(digits_, rhs.digits_, count_ * sizeof(Type));
            }
            return *this;
        }

        BigInteger& operator=(uint64_t u)
        {
            digits_[0] = u;
            count_     = 1;
            return *this;
        }

        BigInteger& operator+=(uint64_t u)
        {
            Type backup = digits_[0];
            digits_[0] += u;
            for (size_t i = 0; i < count_ - 1; i++)
            {
                if (digits_[i] >= backup)
                    return *this; // no carry
                backup = digits_[i + 1];
                digits_[i + 1] += 1;
            }

            // Last carry
            if (digits_[count_ - 1] < backup)
                PushBack(1);

            return *this;
        }

        BigInteger& operator*=(uint64_t u)
        {
            if (u == 0)
                return *this = 0;
            if (u == 1)
                return *this;
            if (*this == 1)
                return *this = u;

            uint64_t k = 0;
            for (size_t i = 0; i < count_; i++)
            {
                uint64_t hi;
                digits_[i] = MulAdd64(digits_[i], u, k, &hi);
                k          = hi;
            }

            if (k > 0)
                PushBack(k);

            return *this;
        }

        BigInteger& operator*=(uint32_t u)
        {
            if (u == 0)
                return *this = 0;
            if (u == 1)
                return *this;
            if (*this == 1)
                return *this = u;

            uint64_t k = 0;
            for (size_t i = 0; i < count_; i++)
            {
                const uint64_t c  = digits_[i] >> 32;
                const uint64_t d  = digits_[i] & 0xFFFFFFFF;
                const uint64_t uc = u * c;
                const uint64_t ud = u * d;
                const uint64_t p0 = ud + k;
                const uint64_t p1 = uc + (p0 >> 32);
                digits_[i]        = (p0 & 0xFFFFFFFF) | (p1 << 32);
                k                 = p1 >> 32;
            }

            if (k > 0)
                PushBack(k);

            return *this;
        }

        BigInteger& operator<<=(size_t shift)
        {
            if (IsZero() || shift == 0)
                return *this;

            size_t offset     = shift / kTypeBit;
            size_t interShift = shift % kTypeBit;
            RAPIDJSON_ASSERT(count_ + offset <= kCapacity);

            if (interShift == 0)
            {
                std::memmove(digits_ + offset, digits_, count_ * sizeof(Type));
                count_ += offset;
            }
            else
            {
                digits_[count_] = 0;
                for (size_t i = count_; i > 0; i--)
                    digits_[i + offset] =
                        (digits_[i] << interShift) | (digits_[i - 1] >> (kTypeBit - interShift));
                digits_[offset] = digits_[0] << interShift;
                count_ += offset;
                if (digits_[count_])
                    count_++;
            }

            std::memset(digits_, 0, offset * sizeof(Type));

            return *this;
        }

        bool operator==(const BigInteger& rhs) const
        {
            return count_ == rhs.count_ &&
                   std::memcmp(digits_, rhs.digits_, count_ * sizeof(Type)) == 0;
        }

        bool operator==(const Type rhs) const
        {
            return count_ == 1 && digits_[0] == rhs;
        }

        BigInteger& MultiplyPow5(unsigned exp)
        {
            static const uint32_t kPow5[12] = {5,
                                               5 * 5,
                                               5 * 5 * 5,
                                               5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5,
                                               5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5 * 5};
            if (exp == 0)
                return *this;
            for (; exp >= 27; exp -= 27)
                *this *= RAPIDJSON_UINT64_C2(0X6765C793, 0XFA10079D); // 5^27
            for (; exp >= 13; exp -= 13)
                *this *= static_cast<uint32_t>(1220703125u); // 5^13
            if (exp > 0)
                *this *= kPow5[exp - 1];
            return *this;
        }

        // Compute absolute difference of this and rhs.
        // Assume this != rhs
        bool Difference(const BigInteger& rhs, BigInteger* out) const
        {
            int cmp = Compare(rhs);
            RAPIDJSON_ASSERT(cmp != 0);
            const BigInteger *a, *b; // Makes a > b
            bool              ret;
            if (cmp < 0)
            {
                a   = &rhs;
                b   = this;
                ret = true;
            }
            else
            {
                a   = this;
                b   = &rhs;
                ret = false;
            }

            Type borrow = 0;
            for (size_t i = 0; i < a->count_; i++)
            {
                Type d = a->digits_[i] - borrow;
                if (i < b->count_)
                    d -= b->digits_[i];
                borrow          = (d > a->digits_[i]) ? 1 : 0;
                out->digits_[i] = d;
                if (d != 0)
                    out->count_ = i + 1;
            }

            return ret;
        }

        int Compare(const BigInteger& rhs) const
        {
            if (count_ != rhs.count_)
                return count_ < rhs.count_ ? -1 : 1;

            for (size_t i = count_; i-- > 0;)
                if (digits_[i] != rhs.digits_[i])
                    return digits_[i] < rhs.digits_[i] ? -1 : 1;

            return 0;
        }

        size_t GetCount() const
        {
            return count_;
        }
        Type GetDigit(size_t index) const
        {
            RAPIDJSON_ASSERT(index < count_);
            return digits_[index];
        }
        bool IsZero() const
        {
            return count_ == 1 && digits_[0] == 0;
        }

    private:
        template <typename Ch> void AppendDecimal64(const Ch* begin, const Ch* end)
        {
            uint64_t u = ParseUint64(begin, end);
            if (IsZero())
                *this = u;
            else
            {
                unsigned exp = static_cast<unsigned>(end - begin);
                (MultiplyPow5(exp) <<= exp) += u; // *this = *this * 10^exp + u
            }
        }

        void PushBack(Type digit)
        {
            RAPIDJSON_ASSERT(count_ < kCapacity);
            digits_[count_++] = digit;
        }

        template <typename Ch> static uint64_t ParseUint64(const Ch* begin, const Ch* end)
        {
            uint64_t r = 0;
            for (const Ch* p = begin; p != end; ++p)
            {
                RAPIDJSON_ASSERT(*p >= Ch('0') && *p <= Ch('9'));
                r = r * 10u + static_cast<unsigned>(*p - Ch('0'));
            }
            return r;
        }

        // Assume a * b + k < 2^128
        static uint64_t MulAdd64(uint64_t a, uint64_t b, uint64_t k, uint64_t* outHigh)
        {
#if defined(_MSC_VER) && defined(_M_AMD64)
            uint64_t low = _umul128(a, b, outHigh) + k;
            if (low < k)
                (*outHigh)++;
            return low;
#elif defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)) &&             \
    defined(__x86_64__)
            __extension__ typedef unsigned __int128 uint128;
            uint128 p = static_cast<uint128>(a) * static_cast<uint128>(b);
            p += k;
            *outHigh = static_cast<uint64_t>(p >> 64);
            return static_cast<uint64_t>(p);
#else
            const uint64_t a0 = a & 0xFFFFFFFF, a1 = a >> 32, b0 = b & 0xFFFFFFFF, b1 = b >> 32;
            uint64_t       x0 = a0 * b0, x1 = a0 * b1, x2 = a1 * b0, x3 = a1 * b1;
            x1 += (x0 >> 32); // can't give carry
            x1 += x2;
            if (x1 < x2)
                x3 += (static_cast<uint64_t>(1) << 32);
            uint64_t lo = (x1 << 32) + (x0 & 0xFFFFFFFF);
            uint64_t hi = x3 + (x1 >> 32);

            lo += k;
            if (lo < k)
                hi++;
            *outHigh = hi;
            return lo;
#endif
        }

        static const size_t kBitCount = 3328; // 64bit * 54 > 10^1000
        static const size_t kCapacity = kBitCount / sizeof(Type);
        static const size_t kTypeBit  = sizeof(Type) * 8;

        Type   digits_[kCapacity];
        size_t count_;
    };

} // namespace internal
RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_BIGINTEGER_H_
